1. Field of the Invention
The present invention relates to a slider unit with a built-in moving-coil linear motor, which has been extensively used in semiconductor and liquid crystal display industries, measuring instruments, assembling machines, machine tools, industrial robots, conveyors and others.
2. Description of the Prior Art
In recent years, multi-axis stages and moving mechanisms such as X-Y plotters employed in the diverse technical fields as described above have required more and more a slider unit, which is compact or slim in construction and light in weight, and moreover able to operate with high propulsion, high speed and high response to provide high speed travel and accurate position control for works, tools, articles and instruments. Linear motors commonly used in the slider units involve two broad types. The first, called moving-magnet linear motor, has a stator of an armature coil arranged lengthwise over the entire length of a bed of stationary part, and a moving-field magnet of permanent magnet arranged on a table movable in a sliding manner along the length of the bed. The second, called moving-coil linear motor, has a stator of field magnet mounted on the bed, and moving-armature coils distributed in space one after another on the table such that they lie a preselected electrical angle out of phase.
A moving-coil linear motor is disclosed in Japanese Patent Laid-Open No. 68365/1993, in which field magnets on a stator are arranged with unlike poles opposing to each other and alternating lengthwise. A slider is mounted to the stator for sliding movement through linear motion guide units. The slider is provided with a moving element having armature coils, which are distributed in space so that their magnetic axes lie 120xc2x0 apart. The armature coils are applied with the currents of U-, V- and W-phases that are 120xc2x0 in the electrical angle out of phase, and therefore a driving force of a desired direction may occur in the moving element by the control of the conducting direction.
Japanese Patent Laid-Open No. 311723/1994 discloses a dc linear motor and a driving unit provided with the same. In the linear motor, the armature coils are joined to the coil boards with machine screws through the intermediate assembling parts, together with the coil yokes that are provided separately to fasten the armature coils and coil boards. Thus, the linear motor is constructed with a series of motor units connected, each of which is composed of at least two armature coils, a combined coil board and circuit board allotted to the set of armature coils. The driving unit may ensure the stroke most suitable for the operating stroke by either increasing or reducing any number of the motor units connected, depending on the apparatus employing the linear motor.
Japanese Patent Laid-Open No. 38503/1994 discloses a moving-coil linear motor, in which permanent magnets are arranged such that the poles on the magnets alternate lengthwise in polarity, and a moving element is arranged for lengthwise movement. The moving element is provided with polyphase coils exposed in a magnetic gap formed on surfaces of the permanent magnets, and field detecting means to control the conducting direction to the polyphase coils. In the prior linear motor, the permanent magnets are arranged spaced apart and another permanent magnets magnetized lengthwise are alternately arranged and fixed between any adjoining first permanent magnets such that any like polarity comes near on their surfaces, thereby proving a continuous row of permanent magnets.
In addition, a moving-coil linear motor is disclosed in Japanese Patent Laid-Open No. 127037/1998, which comprises a stator of integral permanent magnet magnetized such that poles on the magnet alternate lengthwise in polarity, and a polyphase coil arranged for lengthwise movement along the permanent magnet in a magnetic gap shaped by the permanent magnets.
Japanese Patent Laid-Open No. 64487/1993 discloses a positioning table composed of a moving-magnet of permanent magnet attached to a worktable, means for detecting a position of the table, a coil for a stator made conductive depending on the position of the table, and a polyphase motor changing selectively over a conducting direction of electric current.
Moreover, Japanese Patent Laid-Open No. 300721/1993 discloses a linear motor for sliding means, in which a yoke magnet is composed of a upper plate, lower plate and connecting plate, which are prepared separately and then assembled integrally with fixing means such as machine screws. According to this prior linear motor, the parts for the yoke magnet, or the upper plate, lower plate and connecting plate, must be made great in thickness to render less the flexure that might be caused by the attractive force exerted from the opposing magnets. As a result, the sliding means becomes large in height in cross section thereof, thus failing in compactness of the entire apparatus.
For the slider unit having the moving-coil linear motor that is linearly moved together with a worktable by virtue of interaction between magnetic flux generated in a pair of field magnets arranged on confronting inside surfaces of the magnet yoke, each to each surface, and an electric current flowing through an armature coil arranged in a gap provided between the field magnets, thus, an improved linear motor has been desirable, which has the stiffness enough to withstand the attractive force due to the magnet even when the magnet yoke is made less in thickness, so that the slider unit may be made entirely slim or compact in construction and the worktable may operate with highly accurate speed and position control.
The present invention, therefore, has as its primary object to overcome the subject as described just above and more particular to provide a slider unit with a built-in moving-coil linear motor, in which driving means actuated by the moving-coil linear motor is incorporated, and a magnet yoke, despite made less in thickness, is enhanced in stiffness, thereby relieved from possible strain due to the magnetic force so that the slider unit may be reduced overall height to be made slim in construction and also makes it possible to provide accurate speed and position control.
The present invention is concerned with a slider unit with a built-in moving-coil linear motor, comprising a bed supporting thereon a magnet yoke, a table movable through linear motion guide units in a sliding manner with respect to the bed, end plates mounted to lengthwise opposing ends of the bed, each to each end, a pair of field magnets arranged on inwardly confronting surfaces of the magnet yoke in such a manner that poles on the field magnets alternate in polarity along a moving direction of the table and also unlike poles confront each other across an air gap between the field magnets, and a moving-coil assembly mounted to the table and provided with armature coils arranged in the air gap, wherein the moving-coil assembly moves together with the table by virtue of electromagnetic interaction of magnetic flux of the field magnets with current flowing in the armature coils, the magnet yoke is composed of a pair of confronting sections having thereon the field magnets, each to each section, and a connecting section to join the confronting sections to each other at their lengthwise edges extending along the moving direction of the table, and the moving-coil assembly extends into the air gap, with passing through a sidewise opening formed at another edges of the confronting sections extending along the moving direction of the table.
In accordance with an aspect of the present invention, the connecting section is formed integrally with the confronting sections. Moreover, it is preferable that both the table and the bed are made of aluminum alloys.
In accordance with another aspect of the present invention, the bed is composed of a bottom and a pair of upright walls rising at sidewise opposing sides of the bottom and extending along the moving direction of the table, and the magnet yoke is arranged such that any one of the confronting section is mounted on the bottom while another of the confronting sections is spaced apart in substantially parallel with the bottom, with the connecting section extending in perpendicular to opposing surfaces of the confronting sections. Moreover, the table is arranged on top faces of the upright walls for sliding movement with respect to the bed through the linear motion guide units.
In accordance with another aspect of the present invention, there is provided detecting means to monitor a position of the table relative to the bed, the detecting means being installed inside any one of the upright walls of the bed, which is near the sidewise opening of the magnet yoke. In addition, the detecting means is comprised of a linear scale attached lengthwise on an inside surface of the upright wall nearby the sidewise opening of the magnet yoke, and a sensor head provided inside the table to detect the linear scale. As an alternative, the detecting means is of optical type in which the linear scale is a photo-linear scale and the sensor head is an optical sensor head.
In accordance with a further another aspect of the present invention, the table is made therein with a port to permit access to the sensor head.
In accordance with another aspect of the present invention, a slider unit is disclosed, wherein any one of the confronting sections of the magnet yoke, which is near the table, is attached to the bed, while another of the confronting sections is provided by a part of the bed and the connecting section is provided by a part of the former one of the confronting sections and a part of the bed. In the construction described just above, the table is made of aluminum alloys, whereas the bed is made of magnetic material. Moreover, the bed is composed of a bottom and a pair of upright walls rising at sidewise opposing sides of the bottom and extending along the moving direction of the table, and the former one of the confronting sections and the connecting section are provided by a part of the bottom and any one of the upright walls, while another of the confronting sections of the magnet yoke is arranged in substantially parallel with the bottom.
In accordance with another aspect of the present invention, the moving-coil assembly has a coil board extending into the air gap between the field magnets, and the armature coils are a plurality of flat polyphase structures arranged on any one surface of the coil board in juxtaposition along the moving direction of the table.
In accordance with another aspect of the present invention, the armature coils are made with convexities while the coil board has recesses complementary to the convexities, so that the armature coils are fixed to the coil board with adhesive, with the convexities fitting in the associated recesses. This construction can certainly keep the armature coils against changes or slippage in position relative to the coil board regardless of high-speed operation of the table.
In accordance with a further another aspect of the present invention, each armature coil comprises a core member of molded resinous material, and winding turns looped around the core member in the form of flat rectangular solid.
In accordance with another aspect of the present invention, the bed is provided with limiters to define a tolerable range of moving stroke of the table and an origin mark to define a home position of the table, and any one of the table and the moving-coil assembly has a limit sensor to detect the limiters and the origin mark. Monitoring the limiters and/or the origin mark allows controlling the position and/or stroke of the moving table.
In accordance with an additional aspect of the present invention, recesses for manipulation are formed at the outermost end faces of the end plates, thereby making it possible to manually operate the slider unit.
In accordance with another aspect of the present invention, stoppers of elastic body are attached to inside surfaces of the end plates to provide buffers for a collision against the table. Were the table driven over the tolerable range of the stroke in the bed, the elastic stoppers on the inside surfaces of the end plates would buffer the collision with the table to protect the slider unit against breakage.
In accordance with another aspect of the present invention, a slider unit is disclosed wherein a plurality of the tables is arranged to a single bed for sliding movement. Moreover, the adjoining tables has the stoppers of elastic material on their ends facing at least one moving direction of the tables, in order to buff impact of collision between the adjoining tables.
With the slider unit constructed as described just above, electric conduction to the armature coils causes the moving-coil assembly to slide together with the table through the linear motion guides units relatively to the bed by virtue of the electromagnetic interaction of the magnetic flux created by the field magnets with the current flowing through the armature coils.
For example, when controlling the direction of current to the armature coils depending on the direction of magnetic flux, which changes as the moving-coil assembly moves, the propulsion to force continuously the moving-coil assembly towards the desired direction comes into action and thus the table may continue to move in the desired direction. Controlling the quantity of current can realize acceleration and braking, whereas controlling the direction of current makes it possible to the travelling direction of the table. Moreover, the magnet yoke in which the confronting webs are formed integrally with the connecting web is improved considerably in rigidity or stiffness, compared with the yoke in which the confronting webs and the connecting web prepared separately are joined with mechanical fasteners, thus becoming less subject to the deflection owing to the magnetic attraction.
The magnet yoke of the present invention may contribute to saving space for combination with the moving-coil assembly and realizing effective electromagnetic interaction. Moreover, the table may be kept on steady sliding motion relative to the bed by virtue of the paired upright walls.
In a slider unit in which any one of the confronting sections of the magnet yoke is provided by a part of the bed, while the connecting section is provided by a part of another one of the confronting sections and a part of the bed, the bed high naturally in stiffness serves partially as a part of the magnet yoke and only one of the confronting sections is attached directly to the bed. This construction results in enhancing remarkably the stiffness, which might withstand the attractive force due to the magnets, thereby enabling to make less the amount of distortion of the magnet yoke, compared with the conventional magnet yoke assembled with fixing means such as screws. The magnet yoke constructed as described just above may also contribute to saving space for combination with the moving-coil assembly and realizing effective electromagnetic interaction.
The sensor means to detect information as to the positions of the table with respect to the bed is placed near the central area of the table and therefore is less subject to the adverse influence of changes in position such as pitching, yawing and rolling as the table 10 moves, so that the accurate sensing control may be realized. The sensing means is preferably made of optical type, which is more suitable for high accuracy because of relatively poor sensibility to a deviation between the table and the bed. In addition, the table is provided therein with the port for access to the sensor head to make it easy to adequately regulate the position and posture of the sensor head relatively to the linear scale. And since the sensor head is arranged nearby a moving-coil assembly, the wiring for the sensor means may be neatly arranged in a narrow area.
The moving-coil assembly composed of the coil board and flat armature coils is made as slim as possible in thickness and arranged for linear movement in the air gap between the confronting field magnets.
With the armature coils of polyphase structure, the steady electromagnetic interaction with the field magnets can be obtained regardless of the relative position of the table with respect to the bed so that the table may always move steadily.
The armature coils are fixed to and the coil board with adhesive, with the complementary convexities and recesses formed on their facing surfaces coming in engagement with one another. This assures the complete fit of the armature coils on the coil board without causing no slippage between them. Thus, the armature coils can withstand the inertia that might occur as the table moves at high speed, and also very hard to lose their form due to heating.
The core of the molded resinous material is favorable to produce the armature coil strong enough to hold up its configuration. For example, the armature coils, as less subject to deformation even under high temperature, rise in structural strength, thereby allowing higher-speed of operation than any other prior slider units.
As the slider unit, as entirely made in the elongated flat form, may be easily moved and/or carried by putting the operator""s hands on the recesses formed at the outermost end faces of the end plates.
At least the table is made of aluminum alloys. This renders highly light in weight the moving side of the slider unit to obtain high acceleration and braking without considerably powerful electromagnetic prolusion, thereby achieving high speed and high response properties.
In the prior magnet yoke in which the parts produced individually are assembled into the completed yoke unit, it has been very hard to make the yoke reduced in height and, therefore, the slider unit has inevitably become much bulky. In contrast, according to the slider unit constructed as described above, the moving-coil linear motor may be made reduced in height to provide the slider unit, which is much slim or compact in volume. Thus, this slider unit realizes the saving in space for production, storage, conveying, installation and operation thereof and contributes to the improvement in working conditions of the slider units. Moreover, the enhancement in stiffness of the magnet yoke makes it possible to produce at least the table from aluminum alloys. As a result, the linear motor may be made less in weight and high acceleration and braking can be obtained even in the same output compared with the prior linear motor.